Thermostatically operated electric switch



Dec. 5, 1939.

G. H. HART THERMOSIAI'ICALLY OPERATED ELECTRIC SWITCH Filed March 14, 1936 wanaaamfi W 0 t awe rm r 5/ 'l E GEORGE HEGEMANHART Patented Dec. 5, 1939 THERMOSTATICALLY OPERATED ELECTRIC SWITCH George Hegeman Hart, West Hartford, Conn.

Application March 14, 1936, Serial No. 68,842

8 Claims.

This invention relates to thermostatically perated switches for use in controlling temperatures within a chamber or the like. As an instance of a use to which the present invention may be applied, reference may be had to the control of temperature of an electrically heated oven or the like, it being understood, however, that the improved apparatus is not limited to this specific application.

The aim of the invention is to provide an improved device having an expansible and contractible bellows, a switch operated thereby, and means for adjusting the device so that the circuit, will be made and broken at any desired temperatures within a given range of operation, the arrangement being characterized by its simplicity in construction, its compactness in arrangement, its effectiveness in operation, and the ease and facility with which the device'may be adjusted to operate at any desired temperatures.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplifled in the construction hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

In the accompanying drawing, wherein is shown one embodiment which the present invention may take:

Figure 1 is a front elevational view' of the device with parts removed for purposes of illustration;

- Fig. 2 is a side elevational view thereof;

Fig. 3 is a view taken longitudinally and centrally through the device, this view being taken substantially on line 3-3 of Fig. 1;

Fig. 4 is a plan view looking into the switch casing, the cover being removed;

Fig. 5 is a longitudinal sectional view through the apparatus, this viewbeing taken substantially on line 5-5 of Fig. 4, and the switch being shown in open position;

Fig. 6 is a view similar to Fig. 5 but on a reduced scale, and the switch being shown in closed position;

Fig. '7-is a fragmentary view taken transversely through the switch and showing a portion of the expansible bellows, this view being taken substantially along line 1-1 of Fig. 6;

F 8. 8 is 'a fragmentary view looking at the forward end of the housing or cap for the expansible bellows and taken substantially along line 8-8 of Fig. 3; and

Fig. 9 is a perspective view of the operating handle support and calibrating mechanism which also serves to limit the extent of handle movement.

In accordance with my invention, I have provided a thermostatically operated electric switch arranged to automatically control an electrical heating device within a relatively close range of temperature, and, more particularly, a switch which is responsive to temperature changes within a chamber such as the oven of an electric stove. My switch is arranged to make an electric circuit at substantially one predetermined temperature and to break said circuit at substantially another predetermined but slightly higher temperature, the device being adjustable at the will of the operator to maintain any desired mean temperature within the oven or otherchamber the temperature of which is to be controlled. To accomplish this, a bulb containing an expansible fluid is located within the chamber or oven wherein the temperature is to be automatically controlled, and an adjustably positioned floating bellows or sylphon remotely connected thereto is arranged to control the opening and closing of an electric switch whereby the temperatures at which the circuit is made and broken may be predetermined,

Referring more particularly to my' invention as herein illustrated, I have provided a hollow substantially rectangular casing composed of suitable insulating material and having a laterally disposed shelf M at one end thereof. A partition 23 extending longitudinally of and substantially centrally within the casing is provided with a through hole 24 and a pair of transversely extending slots 25 diametrically disposed of said hole and extending through the greater portion of its length, as illustrated in Fig. 3. Hole 24 is arranged to receive the bottom portion or depending stem of a sylphon and a switch actuating member, as win be later described.

A pair of resiliently movable switch arms controlled by the bellows and located in spaced relation in the bottom of the casing on each side of block 23 is suitably secured as by rivets to supporting plates 3| fastened as by screws to of expansion. When electric current flows through such a bimetallic element, it becomes heated, and the unequal expansions of the two strips forming this element cause it to become slightly bowed or deformed.

In the present instance, the metal having the lesser coefficient of expansion is located adjacent to the movable switch arms so that the deformation of these elements will cause them to become bent towards the movable switch contacts, necessitating that said movable contacts be shifted through a slightly greater distance to open the circuit (Fig. 6), thereby providing a slight temperature lag and a consequent few degrees of temperature variation between the opening and closing switch temperatures so that the switch contacts will not tend to flutter and arc, resulting in a frequent burning of the points. It will be appreciated, of course, that the deformed showing of arms 35 has. been greatly exaggerated to better disclose this feature.

In view of the fact that the bellows, which is arranged to regulate the opening and closing of the switch, is also filled with expansible fluid, it will Be evident that local temperature changes adjacent the bellows will also materially affect its expansion and contraction. I have so constructed the present invention as to compensate for these local temperature variations without affecting the range of automatic control within the chamber. To accomplish this, the bimetallic switch arms 35 are constructed to such size and composed of such metals having difierent coeflicients of expansion that under local temperature changes they will bend and move the contacts carried thereby at substantially the same rate and in the same direction as the contacts 34 are moved by the bellows due to the expansion and contraction of the latter under the said local temperature variations, resulting in a similar controlling movement of switch arms 30 irrespective of local temperature changes. In other words, changes in local temperature surrounding the switch points and bellows will not alter the efi'ective opening and closing positions of the switch contacts relative to each other.

A thermostat bulb 38 sealed at one end and to variations in temperature and arranged to expand and contract, causing a resultant expansion and contraction of sylphon 40. The sylphon has an upper expansible bellows portion and a lower projecting cylindrical stem 42 slidably received within hole 24. As best shown n Fig. '7, a substantially T-shaped switch operating member, generally indicated at 43 and composed of insulating material, is located beneath stem 42 for linear movement in such manner that its two laterally extending arms 44 are slidably received within slots 25 overhanging movable switch arms 30, and a downwardly depending tongue portion 45 is received for guiding movement within hole 24. Expansion of the sylphon results in a downward movement of stem 42, causing the arms 44 to engage the resilient switch arms 30 and move the contacts 33 and 34 out of engagement to disconnect the heating circuit within the temperature controlled chamber. When the temperature in the chamber again drops below 'a substantially predetermined point, the sylphon contracts, and the heating circuit is again connected. In view of the fact that the bimetallic switch arms 35 deform in synchronism with the expansions and contractions of the bellows under influence of local temperature changes, it will be appreciated that these arms also serve to compensate for these local temperature changes, and the oven temperatures may be automatically maintained within a substantially predetermined but adjustable temperature range. In this manner, the

temperature is automatically maintained within a substantially predetermined relatively close range of limits. The top of casing 20 is provided with a protecting cover 46, and a substantially cup-shaped housing 41 thereon serves to protect the sylphon and associated parts from injury as well as to support a temperature presetting mechanism, as will be hereinafter described. The housing and cover are secured in position in any suitable manner, as by screws 48 passing through the casing.

To facilitate operation of the making and breaking of the switch contacts at predetermined but adjustable temperatures, the sylphon is resiliently supported upon a coiled spring 49 surrounding stem 42 and located at its lower end by a projecting boss 50 on partition 23. This resilient support maintains the top face 53 of the sylphon in continuous engagement with a movable abutment member 54 in the form of an adjustment screw at one end. Member 54 is threadably received within a threaded portion 55 of housing 41 and substantially axially of stem 42 and arranged for rotary movement under control of a suitable handle 51 which, in the present instance, is composed of a heat resistant insulating material which may be molded to desired form. It will thus be appreciated that rotation of abutment member 54 under control of handle 51 serves to: regulate the movement of sylphon 40 and slidably position stem 42 relative to T-shaped operating member 43, whereby a given expansion of the sylphon as caused by fluid expansion within bulb 38 will engage stem 42 with member 43 to depress arms 44 and open the circuit at a predetermined but adjustable temperature.

Handle 51 is arranged to impart a predetermined extent of rotary movement to abutment 54 and to be adjustably calibrated relative to said member whereby a plurality of spaced legends marked on the flanged portion 58 of the handle and indicating the various temperatures may be selectively aligned with an indexed line 59 on a plate 60 to present the sylphon relative to the switch, causing the switch to open and close at predetermined temperatures. The handle is also provided with an "ofi" position wherein the abutment member 54 may be rotated to depress the sylphon and operating member 43' and hold the switch points in open circuit position. Index plate 60 may be supported in any suitable manner such as by a clamping member 6| engaging housing 41 and having laterally projecting supporting ears 62 secured to the plate. If desired, the index plate may further be located upon a suitable panel 63 associated. with a stove or other electrical apparatus whereby the operative switch parts are hidden from view. It is not believed necessary to illustrate such a mounting in detail since it does not comprise a part of the present invention. The handle 51 is provided with a counterbored axial aperture 54 including two coaxial bores 64a and 54b separated by an intermediate peripheral shoulder 65 and having two diametrically opposed grooves 58 extending the length of said bores. Abutment member 54 is provided above its threaded portion with a reduced concentric hub 68, an adjacent locking shoulder 69, and a reduced upwardly extending coaxial shaft 10.

A substantially cylindrical locking plate ll, having a peripheral Iace slidably received within aperture 64b, is journalled on hub 58 and provided with a downwardly depending finger 12 adapted for limited arcuate movement within a curved slot 13 in the top of housing 41. Plate H is further provided with two diametrically opposed ears 15 adapted to slidably interlock in the opposed grooves 56 whereby the extent of rotary movement of handle 51 will be limited to that of the plate. A disk-shaped calibration plate Tl peripherally received within diameter 641) is provided with a central hole mating with driving shoulder 69 so that the plate is constrained for integral rotation with abutment 54. Plate 11 is further provided with a pair of arcuate adjustment slots 18 arranged to receive a lower reduced threaded portion of a screw 80 threaded within plate ll, as illustrated in Figs. 3 and 9. Hence, it will be appreciated that screw 80 may be loosened for calibration purposes, and plate II and handle 51 may be angularly prelocated with reference to the extent to which the abutment 54 is threaded through housing 41 so that the correct temperature indicating legend on flange 58 is prelocated with reference to index line 59. Thereafter screw 80 may be tightened so that the legends on the handle will locate the end of said screw in its required position relative to the sylphon so that the switch will react to the correct predetermined temperatures.

As shown in Figs. 1 and 3, a locating disk 82 is journalled on shaft above plate 11 and peripherally received within diameter 64a. This disk engages shoulder 65 and is further provided with arcuate apertures 83 adapted to slidably receive screw 8|] therethrough without interfering with its adjustment. A coiled spring 85 surrounds shaft 10 and is provided at its upper end with an elongated substantially U-shaped locking portion 86 arranged to be resiliently received within an annular groove 8! at the upper end of shaft 10. This spring is compressively received in this position to maintain plate 82 in supporting engagement with shoulder 65 so that the handle will be accurately located. The upper end of aperture 64 is provided with a suitable snap cover 88 which may be easily removed to gain access for assembling of parts and calibration purposes.

As many changes could be made in the above construction and many apparently widely dif== ferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim as my invention:

1. In a temperature controlled electric switch, a pair of movable switch arms, an insulating member connecting the same so that they will move substantially in unison, an adjustable screw, a handleat one end of said screw, calibrating means between the handle and screw, a bodily adjustable contractible and expansible bellows interposed between said insulating member and the other end of said screw, said screw being rotatable relative to the bellows, the end of said bellows engaging said screw being normally held against movement and the other end of said bellows associated with said insulating member being adapted to move upon contraction and expansion of the bellows, and a spring normally urging said bellows against the end of said screw.

2. In a temperature controlled switch, a casing, a bimetallic fixed contact arm and a movable contact arm spaced from one another in said casing and engageable to open and closea circuit, an expansible and contractible bellows slidably mounted in said casing and operatively connected to said movable arm to control said circuit, a bulb remotely connected to said bellows, and an expansible fluid in said bulb and said bellows, said bimetallic arm being deflected in response to temperature changes to vary the spacing between said arms and serving to compensate for expansions and contractions of the bellows occasioned by local temperature changes and to provide a temperature leg between the opening and closing of the switch.

3. In a temperature controlled electric switch,

a casing, a switch having a bimetallic contact arm fixed at one end to said casing and provided with a contact at its other end, a movable contact arm carried by said casing and having a contact 4. In a temperature controlled electric switch,

a casing, a switch carried by the casing having a bimetallic contact arm and a movable contact arm spaced from one another, said bimetallic arm deflecting towards said movable contact arm under influence of heat resulting from current flow therethrough to reduce the spacing and delay the openingthereof and returning to its origi-' nal position when the current is disconnected, a bodily movable bellows slidably mounted in the casing for actuating'said movable contact arm, manually operable means for bodily adjusting said bellows and position of the movable contact arm, a remotely positioned bulb, and a fluid in i said bulb and bellows and responsive to temperature changes.

5. In a temperature controlled electric switch, a casing, a switch carried by the casing having a bimetallic contact arm fixed at one end and having a contact at its other end, and a movable contact arm having a contact spaced from and adapted to cooperate with said first contact, a contractible and expansible bellows connected to said movable contact arm and arranged to move the same away irom the fixed contact upon expension, a remotely positioned bulb communicating with said bellows, a fluid in said bulb and bellows responsive to temperature changes, and manually operable means for positioning said bellows and movable contact, said bimetallic arm deflecting towards said movable contact arm upon increase in local temperature changes to compensate for the expansion of the bellows due to such changes and maintain the proper spacing between the contacts, and said bimetallic arm also deflecting towards said movable contact arm under influence of heat resulting from current flow therethrough to reduce the spacing between the contacts and provide a lag between the temperatures at which the switch is made and broken.

6. In a temperature controlled electric switch, a switch casing, a movable switch arm mounted in the casing and arranged to open and close a circuit, an expansible and contractible bellows having a stem at one end, said stem being slidably mounted in the casing and operatively connected to the switch arm, means responsive to temperature changes causing said bellows to expand and contract, an adjustment screw mounted in the casing and engageable with the other end of the bellows, a handle on said screw and adapted to indicate various temperature settings, calibrating means between the handle and screw, and a coiled spring resiliently engaging the bellows adjacent its stem. end and urging the bellows into abutting engagement with the adjustment screw whereby expansions and contractions of the bellows will operate the switch arm to open and close the circuit,

'7. In a temperature controlled electric switch,

a switch casing, a movable switch arm mountedin the casing and arranged to make and break a circuit, a bodily adjustable bellows having a stem at one end, said stem being slidably mounted in the casing and operatively connected to said switch arm, an expansible and contractible fluid in the bellows responsive to variations in temperature, an adjustment screw mounted in the casing and engageable with the other end of said bellows, said screw being rotatable relative to the bellows, a handle on said screw to efiect its adjustment, calibrating means between the handle and screw, and a spring resiliently urging the bellows into abutting engagement with the adjustable screw whereby the bellows may be bodily adjusted to predetermined positions and expansions and contractions of the fluid will result in operation of the switch arm at predetermined temperatures.

8. In a temperature controlled electric switch, a casing, a movable switch arm therein, a bodily adjustable expansible and contractible bellows having a stem at one end slidably mounted in the casing, a remotely positioned bulb, a flexible tube connecting the bulb and bellows, said bulb, bellows, and tube being filled With a thermo-expansive fluid, means connecting the stem end of the bellows to the switch arm, a screw adjustably mounted in the casing and engageable with the other end of the bellows, said screw being rotatable relative to the bellows, a spring surrounding said stem and urging the bellows into abutting engagement with said screw, a handle on said screw arranged to indicate various temperature settings, and calibrating means between the handle and said screw whereby the bellows may be initially positioned and temperature changes in the bulb will result in operation of the switch at predetermined temperatures.

GEORGE HEGEMAN HART. 

